Excimer laser micromachining of oblique microchannels on thin metal films using square laser spot

Excimer laser micromachining of thin metal films with a sacrificial polymer coating is a novel technique that produces features with smooth edges. Using this technique, oblique microchannels are fabricated by workpiece dragging and using a square laser spot, where the axis of traverse of the workpiece is not parallel to the edges of the square laser spot. The microchannels have serrated edges that are particular to the shape of the mask producing the spot. The edge roughness of the channels, machined with a square laser spot of side 100 μm, is found to be most affected by the fluence–spot overlap interaction, and the channel width by spot-overlap and the angle of tilt of the traversed path. Polymer coated metal films underwent close to ideal machining, aided by the clamping action of the polymer layer. Through this technique of machining post polymer coating, the edge roughnesses of the microchannels have been curtailed to less than 10 μm, and channel widths to 150 μm. This technique may be used in fabrication of oblique and circular patterns using excimer laser micromachining with rectangular and square laser spots.     

Huge volume expansion and structural transformation of carbon nanotube aligned arrays during electrical breakdown in vacuum

We observed a huge volume expansion of aligned single walled carbon nanotube (SWCNT) arrays accompanied by structural transformation during electrical breakdown in vacuum. The SWCNT arrays were assembled between prefabricated palladium source and drain electrodes of 2 μm separation on a silicon/silicon dioxide substrate by dielectrophoresis. At high electrical field, the SWCNT arrays erupt into a large mushroom-like structure. Systematic studies with controlled electrical bias show that above a certain field the SWCNTs swell and transform to nanoparticles and flower-like structures with a small volume increase. Further increases in electrical bias and repeated sweeping results in their transformation into amorphous carbon as determined from scanning electron microscopy and transmission electron microscopy (TEM). Cross-sectional studies using a focused ion beam and TEM show the height of a 2–3 nm SWCNT array increased to about 1 μm with a volume increase of ～400 times. Electron energy loss spectroscopy reveals that graphitic sp² networks of SWCNT are transformed predominantly to sp³. The current–voltage measurements also show an increase in the resistance of the transformed structure.     

Epoxidized rice bran oil (ERBO) as a plasticizer for poly(vinyl chloride) (PVC)

With environmental and toxicity concerns becoming more critical, there are increasing efforts to remove phthalates from polymer compounds around the globe more rapidly. Phthalates can be replaced by natural products; in particular, those obtained from vegetable oils and fats. In the present study, a natural-based plasticizer, synthesized by epoxidation of non-toxic rice bran oil (RBO) with peroxy acid generated in situ has been added to poly(vinyl chloride). The influence of various reaction parameters on epoxidation was studied by investigating the reaction ratio, temperature, reaction time and stirring speed. Epoxidized rice bran oil (ERBO) obtained from an optimized reaction condition was analyzed by iodine number and oxirane content. FTIR was used to analyze epoxy group formation. Product ERBO was obtained with 82 % oxirane conversion within 3 h of reaction period. PVC sheets were formulated using a conventional plasticizer di-(octyl) phthalate and was partially replaced by synthesized ERBO. The effect of ERBO addition was tested by mechanical properties (tensile strength, modulus, elongation-at-break, shore D hardness) and compared with commercially available ESBO (epoxidized soybean oil). ERBO presented fairly good incorporation and plasticizing performance, as demonstrated by the results of mechanical properties, exudation, migration tests, thermal stability by thermogravimetric analysis, T _g values as shown by differential scanning calorimetry, replacing about 60 % of the total plasticizer.     

Chemical conversion of PET waste using ethanolamine to bis(2-hydroxyethyl) terephthalamide (BHETA) through aminolysis and a novel plasticizer for PVC

Poly(ethylene terephthalate) (PET) recycling has been carried out by various methods, e.g., mechanical recycling, chemical recycling and energy recovery method. In this study, chemical recycling of PET was carried out by aminolysis using ethanolamine and converted into bis(2-hydroxyethyl) terephthalamide (BHETA). The reaction was performed by varying the PET:ethanolamine ratio, reaction time and catalyst used for waste medical grade bottles of PET. Yield of about 81 % was obtained for PET:ethanolamine ratio of 1:4 (w/w), with 3 h reaction time, at 160 °C with zinc acetate as a catalyst. BHETA was characterized with FTIR, ¹H NMR, and DSC analysis. BHETA was further reacted with heptanoic acid at a molar ratio of 1:2.5. The product obtained was used as a plasticizer for PVC at 5, 10, 15 and 20 parts per hundred (phr) concentration. Thermal and mechanical tests were carried out and the result obtained was compared with the virgin PVC without plasticizer and with conventional plasticizer of PVC, i.e., dioctyl phthalate at 15 phr concentration since new plasticizer showed excellent properties at 15 phr concentration. This newly synthesized plasticizer was completely fused with PVC and in tensile testing helped in increasing the elongation, which was an indication of the plasticization effect shown by this developed material. Glass transition temperature also decreased with an incorporation of the new plasticizer as compared to virgin PVC.     

Up-Conversion in Perovskite Strontium Stannate Nanocrystal Whiskers

We report a simple, eco-friendly facile wet chemical route for the synthesis of pristine and rare–earth metal co-doped (Er/Yb, 10/90, 15/85, 20/80) nano-crystalline, strontium stannate (SrSnO₃) whiskers. It is n-type wide bandgap (~4.1 eV) orthorhombic perovskite semiconductor at room temperature, and reveals increase in band gap with the increase in Er/Yb content (from 4.10 to 4.23, 4.30 to 4.39 eV). The samples exhibited strong emission around 365 nm following band-edge excitation by the wavelength of 290 nm. Further, strong up-conversion emission was observed in visible range at the excitation of wavelength 980 nm. The resistivity values were found to decrease with increase in the dopants Er/Yb concentration due to enhancement of charge carriers.     

Computational coupled large-deformation periporomechanics for dynamic failure and fracturing in variably saturated porous media

The large-deformation mechanics and multiphysics of continuous or fracturing partially saturated porous media under static and dynamic loads are significant in engineering and science. This article is devoted to a computational coupled large-deformation periporomechanics paradigm assuming passive air pressure for modeling dynamic failure and fracturing in variably saturated porous media. The coupled governing equations for bulk and fracture material points are formulated in the current/deformed configuration through the updated Lagrangian–Eulerian framework. It is assumed that the horizon of a mixed material point remains spherical and its neighbor points are determined in the current configuration. As a significant contribution, the mixed interface/phreatic material points near the phreatic line are explicitly considered for modeling the transition from partial to full saturation (vice versa) through the mixed peridynamic state concept. We have formulated the coupled constitutive correspondence principle and stabilization scheme in the updated Lagrangian–Eulerian framework for bulk and interface points. We numerically implement the coupled large deformation periporomechanics through a fully implicit fractional-step algorithm in time and a hybrid updated Lagrangian–Eulerian meshfree method in space. Numerical examples are presented to validate the implemented stabilized computational coupled large-deformation periporomechanics and demonstrate its efficacy and robustness in modeling dynamic failure and fracturing in variably saturated porous media.     

Effects of manufacturing process variables on in vitro dissolution characteristics of extended-release tablets formulated with hydroxypropyl methylcellulose

The purpose of this study was to investigate the effect of three process variables: distribution of hydroxypropyl methylcellulose (HPMC) within the tablet matrix, amount of water for granulation, and tablet hardness on drug release from the hydrophilic matrix tablets. Tablets were made both by direct compression as well as wet granulation method. Three formulations were made by wet granulation, all three having the exact same composition but differing in intragranular:intergranular HPMC distribution in the matrix. Further, each formulation was made using two different amounts of water for granulation. All tablets were then compressed at two hardness levels. Dissolution studies were performed on all tablets using USP dissolution apparatus I (basket). The dissolution parameters obtained were statistically analyzed using a multilevel factorial-design approach to study the influence of the various process variables on drug release from the tablets. Results indicated that a change in the manufacturing process could yield significantly dissimilar dissolution profiles for the same formulation, especially at low-hardness level. Overgranulation could lead to tablets showing hardness-dependent drug-release characteristics. Studies showed that intergranular addition of a partial amount of HPMC (i.e., HPMC addition outside of granules) provided a significant advantage in making the formulation more robust over intragranular addition (i.e., that in which the entire amount of HPMC was added to the granules). Dissolution profiles obtained for these tablets were relatively less dependent on tablet hardness irrespective of the amount of water added during granulation.     

Magnetoelectric Effect in Composites of Magnetostrictive and Piezoelectric Materials

In the past few decades, extensive research has been conducted on the magnetoelectric (ME) effect in single phase and composite materials. Dielectric polarization of a material under a magnetic field or an induced magnetization under an electric field requires the simultaneous presence of long-range ordering of magnetic moments and electric dipoles. Single phase materials suffer from the drawback that the ME effect is considerably weak even at low temperatures, limiting their applicability in practical devices. Better alternatives are ME composites that have large magnitudes of the ME voltage coefficient. The composites exploit the product property of the materials. The ME effect can be realized using composites consisting of individual piezomagnetic and piezoelectric phases or individual magnetostrictive and piezoelectric phases. In the past few years, our group has done extensive research on ME materials for magnetic field sensing applications and current measurement probes for high-power electric transmission systems. In this review article, we mainly emphasize our investigations of ME particulate composites and laminate composites and summarize the important results. The data reported in the literature are also compared for clarity. Based on these results, we establish the fact that magnetoelectric laminate composites (MLCs) made from the giant magnetostrictive material, Terfenol-D, and relaxor-based piezocrystals are far superior to the other contenders. The large ME voltage coefficient in MLCs was obtained because of the high piezoelectric voltage coefficient of the piezocrystals and large elastic compliances. In addition, an optimized thickness ratio between the piezoelectric and magnetostrictive phases and the direction of the magnetostriction also influence the magnitude of the ME coefficient.